Zuoren Nie

Effect of Zn Content on the Microstructure and Properties of Super-High Strength Al-Zn-Mg-Cu Alloys

The microstructure and properties of three different Al-Zn-Mg-Cu alloys with high Zn content (9 wt pct, 10 wt pct, and 11 wt pct, marked as 9Zn, 10Zn, and 11Zn, respectively) were investigated. The strength of alloys increases as the Zn content increases from 9 wt pct to 10 wt pct, while it does not increase any more as the Zn content increases continuously from 10 wt pct to 11 wt pct. The stress-corrosion cracking (SCC) resistance decreases as the Zn content increases from 9 wt pct to 10 wt pct, while it changes unobviously as the Zn content increases continuously from 10 wt pct to 11 wt pct. The elongation and fracture toughness of alloys decrease as the Zn content increases in these Al-Zn-Mg-Cu alloys. The Zn content has little effect on the precipitation reaction of Al-Zn-Mg-Cu alloys that contain the mixture of GP zones, and η′ are the main Matrix Precipitates (MPt) in the peak-aging state, and the mixture of η′ and η are the main MPt in the over-aging state. The amount of MPt and coarse T (AlZnMgCu) phases are shown to increase with the increasing Zn content in Al-Zn-Mg-Cu alloys. The coarse T phases hardly dissolve into the matrix and are the source for the crack initiation, which may be the responsibility for the negative effect on the properties of high Zn content Al-Zn-Mg-Cu alloys.

Microstructure of Al-Ti-B-Er refiner and its grain refining performance

Abstract Al-Ti-B-Er refiner was successfully prepared by CR (contact reaction process), a process based on SHS (self propagating high-temperature synthesis). The microstructure of the alloy was studied by optical microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy-dispersive spectrometry. The results showed that Al-Ti-B-Er alloy was composed of a-Al, block-like TiAl3 and flocked TiB2. Compared with Al-Ti-B refiner, formation of TiAlEr compounds, Er modified the morphology of TiAl3 phase, and dispersed the TiB2 and TiAl3. An excellent grain refining performance was obtained when adding 1 wt.% Al-Ti-B-Er in Al-10Zn-1.9Mg-1.6Cu-0.12Zr alloy, the average grain size was about 40 µm. The refinement mechanism of Al-Ti-B-Er was also discussed. Er changed the morphology of TiAl3, TiB2 phase, the refiner would be more efficient. The decomposition of TiAlEr compounds which released Er refrained the growth of TiAl3 and made TiB2 difficult to aggregate or deposit, therefore resulted in more particles being efficient nucleation substrate.

Plasticity and microstructure evolution of W-CeO2 rods with different short-duration pulse currents

To improve the formability of W-rare earth electrode, the influence of high-energy pulse on the plasticity property of W-CeO2 rods was investigated. The effects of current density (J0), pulse width (tw), frequency (f), and strain rate on the plasticity of W-CeO2 rods were discussed in detail. Results of tensile tests show that the W-CeO2 rods applied with the electrical pulses obtain a maximum percentage total elongation at fracture (9.65xa0%), increased by 118.7xa0% compared to that without pulses. This is owing to both the heat effect and the interaction of current between dislocations and rare earth additions. Electron back scattered diffraction (EBSD)-generated grain boundary (GB) maps suggest that the length of low-angle grain boundaries composed of high-density dislocations decreases after deformation while applying the pulse current. This demonstrates that the short-duration pulsed current enhances the mobility of dislocations. Scanning electron microscopy (SEM) images of the rods after deformation with the pulse current show that the long fiber-shaped additions become discontinuous, which could reduce the stress concentration and hinder the crack propagation.

Geometric and Chemical Composition Effects on Healing Kinetics of Voids in Mg-bearing Al Alloys

The healing kinetics of nanometer-scale voids in Al-Mg-Er and Al-Mg-Zn-Er alloy systems were investigated with a combination of in situ transmission electron microscopy and electron tomography at different temperatures. Mg was observed completely healing the voids, which were then rejuvenated to the alloy composition with further aging, in the Al-Mg-Er alloy. On the contrary, Mg51Zn20 intermetallic compound was formed in voids in the Al-Mg-Zn-Er alloy, which leads to complete filling of the voids but not rejuvenation for the material. For voids with different geometrical aspects, different evolution processes were observed, which are related to the competition between bulk and surface diffusion of the alloys. For voids with a large size difference in their two ends, a viscous flow of surface atoms can be directly observed with in situ electron microscopy, when the size of one end becomes less than tens of nanometers.

Microstructural evolution of new type Al–Zn–Mg–Cu alloy with Er and Zr additions during homogenization

Abstract A comprehensive study on the microstructural evolution of a new type Al–Zn–Mg–Cu–Er–Zr alloy during homogenization was conducted by optical microscope, scanning electron microscope, transmission electron microscopy and X-ray diffraction analysis. The results show that serious segregation exists in as-cast alloy, and the primary phases are T (AlZnMgCu), S (Al 2 CuMg) and Al 8 Cu 4 Er, which preferentially locate in the grain boundary regions. The soluble T (AlZnMgCu) and S (Al 2 CuMg) phases dissolve into the matrix gradually during single-stage homogenized at 465 °C with prolonging holding time, but the residual Al 8 Cu 4 Er phase cannot dissolve completely. Compared with the single-stage homogenization, both a finer particle size and a higher volume fraction of L1 2 -structured Al 3 (Er, Zr) dispersoids can be obtained in the two-stage homogenization process. A suitable homogenization scheme for the present alloy is (400 °C, 10 h)+(465 °C, 24 h), which is consistent with the results of homogenization kinetic analysis.

Microstructure and Mechanical Properties of Hot-Rolled 5E83 Alloy

Hot-rolling plates of Al–4.5Mg–0.7Mn–0.2Zr–0.2Er alloy were prepared under the reduction of 50%, and tensile property, impact toughness were measured at the temperatures varying from 200–470 °C. The microstructure of the hot-rolling plates was investigated using scanning electron microscopy and transmission electron microscopy. The results showed that the tensile strength and yield strength decreased with the rise of the hot-rolling temperature, the elongation and impact toughness showed the opposite trend, and the best match between strength and toughness was at the rolling temperature of 350 °C. The second phase particles in the alloy had a great influence on the impact toughness and plasticity of the alloy. As the rolling temperature increased, the dynamic recovery and dynamic recrystallization occurred in the alloy. Dispersed Al3(Er, Zr) particles formed in the alloy when Er and Zr were added. The Al3(Er, Zr) particles were able to pin dislocation motion, hinder the growth of subgrains and the migration of grain boundaries, thereby inhibited the dynamic recrystallization of Al–4.5Mg–0.7Mn–0.2Zr–0.2Er alloy and its thermal stability improved.

Effect of RRA Treatment on the Properties and Microstructural Evolution of Al–Zn–Mg–Cu–Er–Zr Alloy

Effect of RRA treatment on the mechanical properties and microstructure of Al–Zn–Mg–Cu–Er–Zr aluminium alloy was researched by hardness measurement, conductivity measurement, exfoliation corrosion measurement, transmission electron microscopy (TEM). Discussed the relationship between the regression treatment and composite properties of the alloy. The study found that the hardness of RRA treated alloys first rise and then decline with the increasing of regression time, but the corrosion performance is increasing all the time. After pre-aging treatment 120 °C/24 h, regression treatment 180 °C/60 min, re-aging treatment 120 °C/24 h, the combination property of the alloy is optimal, the hardness, conductivity and the exfoliation corrosion grade are respectively: 207.6 HV, 33.53%IACS, PC. At this moment, it is found from the TEM observations that the matrix precipitates are small and dispersed, resemble to T6 temper. The grain boundary precipitation out phases are discontinuous distribution and the relatively wider PFZ, similar to the T73 temper.